The present invention relates to a method of performing plating of an item having fine parts in rows, and more particularly, but not exclusively, it relates to a method of performing preliminary plating of leads coming out of a flatpack integrated circuit and a support device in the form of a clip for use in such preliminary plating.
A flatpack integrated circuit is a square or rectangular encapsulated integrated-circuit package with leads coming out from two or four sides of the package, in the same plane as the package.
Flatpack IC's are generally interconnected on a printed circuit board by the following procedures: solder cream is applied to selected portions of the circuit board and after placing a flatpack IC on the board, the solder coat is melted either in a reflow furnace or by laser light, thereby soldering the IC to the circuit board. However, with this process, the IC may sometimes be poorly soldered to the circuit board due to the fact that the surfaces of the leads on the flatpack IC are usually made of copper or 42 alloy (Fe - 42% Ni alloy), and they may become oxidized or otherwise fouled so as to result in a solder-repelling state if the IC is left to stand for a prolonged period after fabrication. This problem is particularly serious with the 42 alloy which is inherently low in solderability and is prone to cause unsatisfactory soldering. Therefore, in order to ensure reliable soldering of flatpack IC's, the leads are usually plated with a preliminary solder film.
Preliminary plating of the leads of a flatpack IC is usually performed by dipping the IC into a liquid flux bath followed by a molten solder bath. However, a single flatpack IC has a large number of leads (as many as 100 leads if 25 leads come out from each of the four sides, each side extending about 1-2 cm) at very close intervals, e.g. 0.4-0.8 mm, and a "bridge", i.e. a solder deposit spanning two adjacent leads, will form if the leads are simply dipped into a bath of molten solder. Formation of "bridges" may be prevented by the air knife dipping method in which a flatpack IC emerging from a bath of molten solder is immediately blasted with compressed air so as to blow off excess solder. However, in this method, the solder which is blown off one flatpack by the compressed air may be redeposited on other flatpack IC's in the neighborhood, thereby forming "bridges" on those neighboring IC's or impairing their appearance.